[Feature] - Human readable information about used bandwidth of an instance

[steinex]

Is your feature request related to a problem? Please describe. It's unnecessarily hard to get the used bandwidth of an instance in a humal readable form.

Describe the solution you'd like A USED BANDWIDTH field in Megabyte in vultr-cli instance get analog to ALLOWED BANDWIDTH.

Describe alternatives you've considered Right now the alternative is calculating all the values in vultr-cli bandwidth which IMHO is unnecessarily hard.